java - 变量改变我的单例对象内的状态

Question

我有一个单例对象负责启动和停止 http 服务器(使用 RESTlet 框架)。

当我创建对象时，boolean var isStarted 设置为 false。服务启动时，isStarted 设置为 true。

这是我的单例代码:

private WebService() {
    this(Protocol.HTTP, DEFAULT_PORT);
}

private WebService(final Protocol protocol, final int port)
{
    this.protocol = protocol;
    this.port = port;
    this.isStarted = false;

    // Creating a new Restlet component and 
    this.component = new Component();
}

public synchronized static WebService getInstance()
{
    if(instance == null)
    {
        return new WebService();
    }

    return instance;
}


public synchronized static WebService getInstance(final Protocol protocol, final int port)
{
    if(instance != null)
    {
        instance = null;
    }

    return new WebService(protocol, port);
}

现在我只使用 getInstance()，不带任何参数。

以下是我启动和停止服务器的方法:

public synchronized boolean startServer(final Context context)
{
    if ( isStarted ) {
        Log.d(TAG, "Tried to start a running server");
        throw new IllegalStateException("Tried to start a running server");
    }

    // Add a http connector to the component.
    component.getServers().add(protocol, port);
    component.getClients().add(Protocol.FILE);  

    // Static content
    // Attach the component to the localhost
    ipAuthenticator = new IPAuthenticator(org.restlet.Context.getCurrent());
    ContactsRouter contactsRouter = new ContactsRouter(context, ipAuthenticator);
    AuthenticationRouter authenticationRouter = new AuthenticationRouter(contactsRouter, ipAuthenticator);
    component.getDefaultHost().attach(authenticationRouter);

    // Start it! The HTTP server connector is also automatically started. 
    try {
        component.start();
    } catch (Exception e) {
        Log.e(TAG, e.getMessage());
        isStarted = false;
        return false;
    }

    isStarted = true;
    Log.d(TAG, "Server Started! and isStarted is: " + isStarted);

    return true;
}

public Boolean stopServer()
{
    Log.d(TAG, "WebService: isStarted: " + isStarted);
    if(isStarted)
    {
        try {
            component.stop();
            Log.d(TAG, "Server stopped");
            return true;
        } catch (Exception e) {
            Log.e(TAG, "Exception - Could not stop the server!");
            e.printStackTrace();
        }
    }

    return false;
}

我的问题是，当我使用应用程序用户界面启动和停止服务器时，我可以毫无问题地启动它，但是当我尝试停止服务器(启动后)时，我不能，因为 isStarted 应该是 true 时却是 false，因为我之前刚刚启动了服务器。

这是当我尝试使用我的应用程序 Uuser 界面启动/停止服务器时:

public HttpServer(ProgressBar progressBar, Context context, boolean isChecked)
{
    this.progressBar = progressBar;
    progressBar.setEnabled(false);
    this.context = context;
    webService = WebService.getInstance();
    this.isChecked = isChecked;
}

(...)

@Override
protected void onPostExecute(Void result) {
    // Hide the progress bar
    progressBar.setVisibility(View.GONE);

    // Here in this logcat I receive-> is sever started?: **false** but it should be true
    Log.d(TAG, "isChecked = " + isChecked + " || Is the server started?: " + webService.isStarted()); 

    if(isChecked == true)
    {
        Log.d(TAG, "Going to start the server");
        webService.startServer(context);
    }
    else
    {
        Log.d(TAG, "Going to stop the server");
        webService.stopServer();
    }
}

我的问题是，为什么在服务器启动后，isChecked 应该为 true 时却为 false？

谢谢!

Answer 1

您不会影响单例对象

public synchronized static WebService getInstance()
    {
        if(instance == null)
            instance = new WebService();
        return instance;
    }